Simulations For The GaN HEMT With The Multilayer Heterostructures

As third-generation semiconductor material,GaN material has become a hot research topic because of its wide bandgap,high mobility and low intrinsic carrier concentration.Conventional singlelayer heterojunction device always occupies the core position of GaN based device because of its simple structure and excellent performance.With the increasing demand for device power consumption,the conventional multilayer heterojunction device with lower power consumption has also been widely studied.However,the threshold voltage of conventional multilayer heterostructure device is negative,which greatly limits its daily application.In addition,the electric field concentration will appear at the gate edge of the conventional multilayer heterojunction device,which makes the electric field of the electron channel reache the critical breakdown electric field prematurely and breaks down in advance.In view of the above problems,a novel multilayer heterostructure GaN HEMT with concave gate is studied in this paper,and its advantages are verified by comparing with the conventional singlelayer heterostructure GaN HEMT.Research indicates:the concave gate in the novel multilayer heterostructure device can effectively modulate the on-state characteristics of the device;when the parameter d(the distance from the concave gate to the bottom of the Al GaN barrier layer)is 2nm,compared with the conventional singlelayer heterostructure device,The on resistance of the novel multilayer heterostructure device is reduced by about 13%,and the threshold voltage is increased by about 3V;When the device is withstanding voltage,in the novel multilayer heterostructure device,the GaN modulation layer structure can effectively assist in the depletion of electrons in the channel layer,which can significantly improve the breakdown voltage of the device;for example,compared to conventional singlelayer heterojunction device,the breakdown voltage of the novel multilayer heterojunction device is increased by nearly 5 times when the gate-drain spacing is 3?m.By optimizing the structure parameters of the novel multilayer heterostructure device,it is found that the parameter d has a great influence on the electrical characteristics of the novel multilayer heterostructure device.The smaller the parameter d,the higher the threshold voltage and the stronger the gate control ability;the larger the parameter d,the higher the breakdown voltage of the device.In order to balance the on-state and blocking state characteristics of the device,a novel multilayer heterojunction device with both field plate and concave gate is studied.This device can further optimize the electric field distribution at the electrode edge,which makes the device obtain higher threshold voltage and breakdown voltage when the parameter d is small.Compared with the novel multilayer heterojunction device without field plate,the optimized breakdown voltage of the novel multilayer heterojunction device is increased by about 16.5%when the gate-drain spacing is3?m.In order to obtain the forward threshold voltage,this paper also proposes an enhanced high-voltage multilayer heterojunction device with P doping based on the novel multilayer heterojunction device with both field plate and concave gate.The simulation results show that when the doping concentration of the device exceeds 9?10¹⁸cm^-3,the threshold voltage of the device is gradually stable at about 1.2V.